As shown in FIG. 1, a conventional motor structure includes a rotor 10, in which its center is stationarily coupled to one end of a spindle 11, and the other end is a spindle nose 12 having a necking 13 with a smaller outer diameter; a base 20 having a shaft tube 21 and a stator set 26 disposed thereon, in which the shaft tube 21 can be assembled or integrally formed on the base 20 and an abrasive pad 22, a limit member 30, a bearing 23 and a washer 24 are disposed therein, a position member 25 corresponds to the top end of the shaft tube 21 and caps thereon so as to steadily position the bearing 23, the limit member 30, etc. inside the shaft tube 21, and the stator set 26 is located on the periphery of the shaft tube 21 and can be chosen from either a radial winding type or an axial winding type structure.
A plurality of limit protrusions 31 are extended from the angular periphery of the limit member 30 to the center thereof in a radial manner, such that a groove (not shown in FIG. 1) is formed between every two neighboring limit protrusions 31 and a snap hole 32 is centrally formed within each limit protrusion 31.
Hence, while assembling the rotor 10 and the base 20, the spindle 11 of the rotor 10 needs to first penetrate the position member 25, the washer 24 and the bearing 23. Because the diameter of the snap hole 32 of the limit member 30 is slightly less than the outer diameter of the nose 12 of the spindle 11 as shown in FIG. 2(A), a larger force shall be exerted on the nose 12. Moreover, the groove formed between every two neighboring limit protrusions 31 forces the limit protrusion 31 to deform and make the snap hole 32 expand as shown in FIG. 2(B), so as to facilitate the nose 12 to pass through the snap hole 32, and then the limit protrusions 31 further return to snap the necking 13 so as to limit axial displacement of the spindle 11 with respect to the shaft tube 21 and prevent the rotor 10 from dropping.
Whereas, while the limit protrusions of the limit member are compressed by the nose of the spindle and the snap hole is forced to expand, the limit protrusions are subjected to an excessively bending and deforming angle, which gives rise to the following shortcomings;
Irrecoverable angle of the deformed limit protrusions: The material employed by the limit member shall possess hardness with at least a certain level; otherwise, axial displacement of the spindle cannot be reliably restrained, and thus occurrence of rotor drop becomes inevitable. Meanwhile, such requirement also makes the limit protrusion less flexible. The limit protrusion of the conventional limit member structure forms a right included angle (90°) with an angular periphery such that each limit protrusion exhibits a horizontal pattern. Therefore, when the limit protrusions are subjected to compression applied by the nose of the spindle and are deformed, the angle of the limit protrusion between an original position and a crooked and deformed position is approximately 45°, making the limit protrusions irrecoverable to their original angle, as shown in FIG. 2(C), after the limit protrusions are deformed.
Fracture of the limit protrusion due to excessive deformation: As mentioned in last paragraph, to take the basic strength of the limit member itself into account and prevent rotor drop, a harder material shall be selected. Accordingly, as a result of insufficient flexibility, the limit protrusions are impossible to recover to their original angle after they are subjected to compression of the spindle nose and deformed or even results in fracture of the limit protrusion as shown in FIG. 2(C).
Huge vibrational noise during rotor rotation: A space is designed between the limit member and an abrasive pad inside the shaft tube for the motor structure to store lubricant; after the limit protrusion of the conventional limit member structure is broken, the broken limit protrusion will drop in the lubricant storage space and is attached to the spindle nose due to the viscosity of the lubricant; consequently, the broken limit protrusion accompanies with the spindle to keep churning and colliding in the course of rotation of the spindle, thus resulting in noise and blockage against rotational smoothness of the spindle and rotational vibration of the rotor.
Easy rotor runout: While the rotor is rotating, a reaction force will make the rotor generate an ascending buoyancy force; the limit protrusions are used to snap the necking so as to prevent the rotor from dropping; meanwhile, the limit protrusions urge against the end face of one side of the necking near the nose as shown in the position marked by the broken line in FIG. 2(C). As such, when a portion of the limit protrusion of the conventional limit member is broken, the urging force against the end face is out of balance, thereby making the rotor generate rotation runout.
Easy rotor drop: When one portion of a limit protrusion of the conventional limit member structure is broken, in addition to the rotation runout of the rotor, the overall strength of the limit protrusion is relatively reduced. Once the motor structure is subjected to impact of external force, the occurrence of rotor drop easily takes place.
As a consequence, to completely tackle the issue intrinsic to the above-mentioned conventional limit member structure, a limit structure of motor spindle with a brand new idea must be aggressively conceived and developed to resolve rotor runout, vibrational noise and rotor drop.